Frequently, in chemical processes as well as in other applications, metering pumps are particularly useful. Pumps of this nature often have a diaphragm, one side of which is in direct contact with the fluid that is to be pumped. On the other side of the diaphragm, hydraulic pressure pulses produced by a piston pump cause the diaphragm to flex. The diaphragm produces both a depth or range of flexure and a flexing frequency that is predetermined through the operation of the piston pump. In these circumstances, the diaphragm positively displaces the fluid being pumped as a consequence of this flexing, the volume output from the diaphragm pump being directly related to the range and speed of the piston pump travel of the pump to which it is coupled. Clearly, the capacity of a metering pump is subject to regulation, in large measure, through the control of the driving hydraulic piston pump.
One technique for regulating metering pump capacity through the operation of the hydraulic piston pump is to control the length of the piston's stroke. Illustratively, a motor driven connecting rod is not coupled directly to a wrist pin in the piston in the manner that usually characterizes most fixed displacement reciprocating piston pumps. The connecting rod in this instance is pivotally connected to a tubular housing which swings in an oscillatory fashion due to the influence of said connecting rod. One end of a second connecting rod joins a threaded adjustment screw to a wrist pin within a slide block. Turning the adjustment screw within the oscillating housing shortens or lengthens the linear stroke of the piston by decreasing or increasing the distance from the housing oscillitory axis to the wrist pin, which joins the connecting rod at the adjustment screw, to the pivot point of the oscillating housing. It is, of course, this selective control of the length of the piston stroke that determines a particular output from the piston pump and hence the immediate metering pump output.
In order to enable the adjustment screw to be turned to regulate the piston stroke length, it is usual to mount one end of the screw in the housing. A driven gear in a pair of bevel gears is fixed to the mounted end of the adjustment screw. The driving bevel gear, moreover, is rotated in response to the operation of a shaft which has one fixed universal joint, an oscillating universal joint and a slip shaft. Thus, rotation of the shaft has, through the meshed bevel gears, the net effect of rotating the adjustment screw, and thereby effectively increasing or decreasing the piston stroke. This particular combination establishes a linear or directly proportional relationship between the rotation of the shaft and the change in piston stroke length through the complete range of metering pump capacity range.
The motion of the oscillating housing during pump operation produces a certain amount of reciprocating linear movement of the universally jointed shaft. The slip joint on the shaft absorbs this reciprocating motion to enable a manually operated handwheel to provide the necessary shaft rotation and pump output adjustment. Adjustment during the discharge cycle of the piston pump's stroke requires a great deal of force. The force required in larger capacity metering pumps moreover, being so great that manual adjustment becomes awkward.
Pneumatic, electric and hydraulic devices also have been developed to provide an automated system of pump capacity adjustment. These pneumatic, electric and hydraulic systems, are relatively expensive and require a separate electric, pneumatic or hydraulic motor or pneumatic or hydraulic cylinder, or the like for rotating the shaft or moving the slide block a suitable amount to produce a desired metering pump output.
Accordingly, there is a need for a reliable and inexpensive means for adjusting the capacity of a metering pump.
It is thus an object of this invention to provide a reliable and relatively inexpensive technique for regulating metering pump output without the need for excessive external power.